1. Field of the Invention
The present invention relates to active water compatible energy curable compositions containing a maleimide derivative, useful for preparing various coatings, printing inks, surface finishes, moldings, laminated plates, adhesives, and binders. More specifically, the present invention relates to active water compatible energy curable compositions, which can be cured in the absence of a photoinitiator with an irradiation source of practical intensity and energy value.
2. Description of Related Art
An active energy curable composition polymerized under irradiation of active energy such as thermal energy, ultraviolet light, visible light, and the like, has an advantage of being rapidly cured. Active energy curable compositions are widely used as paints, inks, adhesives, coatings, and the like. However, conventional ultraviolet active energy curable compositions cannot initiate polymerization alone upon irradiation with an energy source; it is therefore necessary to use a photoinitiator. When photoinitiators are used in large quantities, curing progresses rapidly, which encourages the use of large quantities of photoinitiator.
Photoinitator compounds having an aromatic ring are used in general because they effectively absorb ultraviolet light. However, these compounds cause problems such as the yellowing of the cured materials upon addition of heater light. Moreover, low molecular weight energy curable monomers and oligomers, commonly used as photoinitiators because of their solubility a property necessary to initiate photopolymerization effectively, unfortunately have high vapor pressures. Therefore, they tend to give off unpleasant odors at temperatures ranging from room temperature to 150xc2x0 C. Because infrared light, for example, is generated from an ultraviolet energy source, active energy curable compositions are heated substantially upon contact with such light sources. The heating problem is magnified when the ultraviolet light lamps are arranged and used in a side-by-side fashion. The unpleasant odors given off from the photoinitiator result in an unhealthy working environment.
Unreacted or decomposed photoinitiators remain behind in conventional energy curable compositions even after exposure to irradiation by the active energy cure source. These unreacted or decomposed photoinitiators cause problems such as changing the color of the cured film to yellow, unpleasant odors, and the like, when the cured film is exposed to heat or light. For example, when a material at high temperature, such as a thermal head, contacts an active energy curable composition comprising photoinitiator, strong unpleasant odors are given off. Finally, when these cured compositions are contacted by water after irradiation; unreacted photoinitiator is exuded; therefore causing the active energy curable composition to be unsuitable for food packaging applications.
In solving some of these problems, the prior art presents many options. For instance, JP-A-58-89609 discloses an energy curable resin comprising a polymer with polymerizable unsaturated acrylic group and an organic solvent-soluble styrene containing an acrylic thermoplastic resin that does not need a photoinitiator.
WO 89/05827 teaches photopolymerizable adhesive compositions comprising a copolymer of methacrylate monomer and/or methyl acrylate and a photopolymerizable monomer. These photocurable compositions, however, cannot be sufficiently cross-linked by practical irradiation energy sources.
U.S. Pat. No. 5,446,073 and Polymer Preprints, Vol. 37, No. 2, pp. 348-49, 1996 disclose a photopolymerizing method in which maleimide type materials are mixed with vinyl ethers and acrylates to produce a tough film. The polymerization mechanism involves a charge-transfer complex, which is formed by an electron acceptor and an electron donor. However, many of the maleimides are solid and are hardly dissolved in acrylates.
Polymer Letters, Vol. 6, pp. 883-88, 1968 reports that maleimide derivatives can be polymerized in the absence of photoinitiators under irradiation by ultraviolet light. Japanese Patent Applications JP-A-61-250064, JP-A-62-64813, and JP-A-62-79243 teach energy curable compositions comprising maleimide derivatives such as alkylmaleimides and arylmaleimides. However, these maleimide derivatives show low photoinitiator properties, therefore making it necessary to use substantial amounts of photoinitiator in the maleimide compositions.
U.S. Pat. No. 3,920,618 and Japanese Patent applications JP-A-50-123138 and JP-A51-47940 disclose photopolymerizable polymers having an xcex1-aryl substituted maleimide group at a side chain. It is well known that these pendant type maleimides can be crosslinkable by ultraviolet irradiation (i.e. 2+2 photocycloaddition reaction). U.S. Pat. No. 4,079,041 and Europe Patent 21019 teach polymers having side chain type maleimide groups with alkyl substituents. However, these pendant type maleimides cannot be used to form linear polymers by photopolymerization. Therefore they are most commonly used to prepare negative printing plates. In addition, the photocross-linking dimerization reaction takes a rather long time (several tens seconds to several minutes) even with an excess amount of irradiation energy.
Polymer Materials Science and Engineering, Vol. 72, pp. 470-72, 1995 and Proceedings of RadTech Europe 95, pp. 34-56, 2995 disclose photocurable compositions comprising maleimide derivatives as electron acceptors and vinyl ethers as electron donors. The photopolymerizable compositions 1,4-bis (vinyloxymethyl) cyclohexane and N-cyclohexylamalemide or 4-hydroxybutyl vinyl ether and N-(hydroxyalkyl) maleimide, illustrated in these documents are polymerized upon ultra violet irradiation in the absence of a photoinitiator. However, hardening of the coated films does not occur; i.e. the coated films maintain liquid states after ultraviolet irradiation.
WO 98/07759 describes energy curable compositions wherein water-soluble maleimides are copolymerized with acrylates in the absence of water to produce a cured film.
The polymerizing methods described above share numerous problems, which can be summarized as the need for high irradiation intensity to cure sufficiently; the maleimide derivatives being solid at ambient temperature which does not suggest whether they are or can be homo-polymerized upon irradiation in the absence of a photoinitiator; difficulty in obtaining cured coating with practical properties and given the wide range of curable composition disclosed; the need for higher irradiation energy than practical for cross-linking (photodimerization). However, none of these references describe active energy curable compositions containing water or energy curable compositions that are water compatible.
It is an object of the present invention to provide active water compatible energy curable compositions which do not contain photoinitiator, cause unpleasant odors upon curing or cause yellowing, or exude materials from the cured film upon contact with water or solvent. Another object of the present invention is to provide an active water compatible energy curable composition which be photopolymerized by an energy source of practical intensity and energy value and results in coatings that exhibit cure rates, gloss, hardness and solvent resistance values comparable to these of conventional energy cure systems employing photoinitiators.
The present invention is an active water curable energy curable composition comprising a water compatible compound, water and a maleimide derivative represented by the Formula (1): 
wherein n and m each independently represent an integer of 1 to 5, and the sum of m and n is 6 or smaller;
R11 and R12 each independently represent a linking group selected from the group consisting of a straight or branched chain alkylene group, an alicyclic group, an arylalkylene group, and a cycloalkylalkyene group. The arylalkylene group and the cycloalkyl alkylene group may have an aryl or cycloalkyl group as a main chain or a branched chain, respectively;
G1 and G2 each independently represent ester linkage represent by xe2x80x94COOxe2x80x94 or xe2x80x94OCOxe2x80x94 and;
R2 represents a linking chain having an average molecular weight of 100 to 100,000 selected from the group consisting of (poly)ether and (poly) ester linking chains, in which at least one group consists of a group or groups selected from a straight or branched chain alkylene group, an alkylene group having a hydroxyl group, an alicyclic group, an aryl group, and an arylalkylene group; and connected via at least one linkage selected from the group consisting of an ether and ester linkage.
The active water curable energy curable compositions of the present invention contain a maleimide derivative of Formula 1 mentioned above. As for variables R11 and R12 of Formula 1, examples R11 and R12 suitable for use in the present invention include straight alkylene groups such as methylene group, ethylene group, trimethylene group, tetramethylene group, pentamethylene group, hexamethylene group, heptamethylene group, octamethylene group, nonamethylene group, decamethylene group, undecamethylene group, dodecametheyine group, and the like; alkylene groups having a branched alkyl group such as 1-methylethylene group, 1-methyl-trimethylene group, 2-methyl-trimethylene group, 1-methyl-tetramethylene group, 2-methyl-tetramethylene group, 1-methyl-pentamethylene group, 2-methyl-pentamethylene group, 3-methyl-pentamethylene group, neopentyl group, and the like; alicyclic groups such as cyclopentylene group, cyclohexylene group and the like; arylalkylene groups having an aryl group at a main chain or a side chain such as benzylene group, 2,2-diphenyl-trimethylene group, 1-phenyl-ethylene group, 1-phehyl-tetraethylene group, 2-phenyl-tetraethylene group, and the like; cycloalkyl-alkylene group having an alicyclic group at a main chain or a side chain such as cyclohexyl-methylene group, 1-cyclohexyl-ethylene group, 1-cyclohexyl-tetraethylene group, 2-cyclohexyl-tetraethylene group, and the like. However, there are no particular limitations placed on these groups. When the average molecular weight of R2, as a (poly)ether or (poly)ester linking chain is less than 100, curing properties of the maleimide thereof are worse. Even if the compositions are cured, the [gel fraction] of the energy cured composition tends to be lower.
The gel fraction is the percentage of material remaining after a cured film has been refluxed, for example, in methyl ethyl ketone for 3 hours at 80xc2x0 C., then dried at 100xc2x0 C. for one hour. A cured maleimide derivative or composition, which has a 99.8% gel fraction, indicates that only 0.2% of the matrix was solubilized by the above reflux conditions. (i.e. a high degree of conversion).
The percentage conversion is defined as the ration of functional groups to a crosslinked matrix monitored by the disappearance of and IR absorption band during the course of 20 irradiation. This real time IR measurement allows one to quantify percent conversion and provides insight into the reactivity the composition during irradiation.